Material dispenser control circuit with false trigger prevention

ABSTRACT

A control system for turning on and off apparatus which discharges material onto objects moving on a conveyor past an article sensing and material dispensing station. An article sensor, including an incandescent lamp and a phototransducer spaced on opposite sides of a conveyor, senses movement of an article beneath a material dispensing valve as the article interrupts a light beam projecting across the conveyor from the lamp to the phototransducer. A threshold detecting circuit, including an operational amplifier and a single-shot, responds to the change in light intensity on the phototransducer occasioned by interruption of the light beam to energize a solenoid which controls operation of the material dispensing valve. A power supply including a full-wave rectifier and a smoothing capacitor provide power for the circuit components. A switch in the energization path of the solenoid, which is opened when the main ON/OFF power switch located between the rectifier and a conventional 60Hz source is opened, prevents discharge of energy from the smoothing capacitor to the solenoid to actuate the dispensing valve when the threshold detector faslely cycles as the incident light on the photocell decreases when the lamp is de-energized by open-circuiting the ON/OFF switch. A capacitor connected between the phototransducer input line to the operational amplifier and the power supply alters the potential of the reference input to the operational amplifier such that the signal output from the phototransducer to the operational amplifier temporarily existing after the ON/OFF switch has been closed and prior to build-up of the incandescent lamp intensity to its normal level does not falsely trigger the operational amplifier and in turn cycle the solenoid and material dispensing valve.

United States Patent 1 Algeri [111 3,862,414 5] Jan. 21, 1975 MATERIALDISPENSER CONTROL CIRCUIT WITII FALSE TRIGGER PREVENTION [75] Inventor:Harvey R. Algeri, North Olmstead,

Ohio

[73] Assignee: Nordson Corporation, Amherst,

Ohio

[22] Filed: Jan. 17, 1974 [21] Appl. N0.: 434,034

[52] US. Cl. 250/206, 250/223 [51] Int. Cl. I-IOIj 39/12 [58] Field ofSearch 250/206, 214, 222, 223;

Primary ExaminerJames W. Lawrence Assistant Examiner--D. C. NelmsAttorney, Agent, or Firm-Wood, Herron & Evans 1 1 ABSTRACT A controlsystem for turning on and off apparatus which discharges material ontoobjects moving on a conveyor past an article sensing and materialdispensing station. An article sensor, including an incandescent lampand a phototransducer spaced on opposite sides of a conveyor, sensesmovement of an article beneath a material dispensing valve as thearticle interrupts a light beam projecting across the conveyor from thelamp to the phototransducer. A threshold detecting circuit, including anoperational amplifier and a single-shot, responds to the change in lightintensity on the phototransducer occasioned by interruption of the lightbeam to energize a solenoid which controls operation of the materialdispensing valve. A power supply including a full-wave rectifier and asmoothing capacitor provide power for the circuit components. A switchin the energization path of the solenoid, which is opened when the mainON/OFF power switch located between the rectifier and a conventional60Hz source is opened, prevents discharge of energy from the smoothingcapacitor to the solenoid to actuate the dispensing valve when thethreshold detector faslely cycles as the incident light on the photocelldecreases when the lamp is de-energized by open-circuiting the ON/OFFswitch. A capacitor connected between the phototransducer input line tothe operational amplifier and the power supply alters the potential ofthe reference input to the operational amplifier such that the signaloutput from the phototransducer to the operational amplifier temporarilyexisting after the ON/OFF switch has been closed and prior to build-upof the incandescent lamp intensity to its normal level does not falselytrigger the operational amplifier and in turn cycle the solenoid andmaterial dispensing valve.

7 Claims, 1 Drawing Figure LIGHT K M l 77 Patented Jan. 21, 1975 I I I Il l i I M DARK g K afim M I LIGHTI MATERIAL SOURCE MATERIAL DISPENSERCONTROL CIRCUIT WITH FALSE TRIGGER PREVENTION This invention relates tocontrol circuits for material dispensing apparatus of the type wherein amoving article interrupts a light beam from an incandescent lamp tocause the control circuit to actuate the material dispenser, and moreparticularly to acontrol circuit of such type incorporating means toprevent false triggering of the control circuit and operation of thedispenser when the control circuit is turned on and/or turned off.

In many automated manufacturing operations, articles move on a conveyorpast a station in which material is dispensed to the moving article. Forexample, in automated paint spraying operations, articles suspended froma moving conveyor are provided with a coating of paint as they passthrough a paint spray coating station. In other automated productionlines, adhesive is applied to, for example, a flap of a box whichsubsequently will be folded to adhere it in place, as the box passesthrough a glue application station. In either type operation, materialis dispensed to an object as it passes through a material dispensingstation. Obviously, if such material dispensing operation is to beautomated, article sensing means must be provided to sense when thearticle is located proximate the material dispenser.

One common form of article sensing means is predicated on the sensing ofthe interruption of a light beam by an article moving on a conveyor. Inarrangements of this type, a source of light and a phototransducer arepositioned on opposite sides of the path of the moving objects such thatas the objects move down the production line they interrupt the lightbeam proximate the material dispensing apparatus. Interruption of thelight beam causes the phototransducer, which previously had beenincident with a relatively high level light intensity from the lightsource, to now be incident with relatively low intensity light. Thischange in received light intensity by the phototransducer is detected bya suitable control circuit causing actuation of the material dispenser.

In article sensing control circuits of the foregoing type whereininterruption of a light beam by a moving article causes material to bedispensed, a problem has resulted in that material is dispensed as anincident to turning on and turning off the photosensing circuitry.Specifically, the problem involves the false triggering of thephotosensing dispenser control circuit during turnon and turn-off whenin fact no article is present on the conveyor to receive the dispensedmaterial, with the result that dispensed material is undesirably placedon the conveyor itself rather than on an article interrupting a lightbeam which is normally the case.

The false triggering which results during turn-on is atrributable to thefact that, for practical reasons, the light source is usually anincandescent lamp which takes a finite time after turn-on to reach itsrelatively high normal intensity level. While the intensity of the lightbeam is building up as the filament of incandescent lamp heats, butbefore it reaches its normal relatively high intensity level, thephototransducer is incident with a relatively low level light intensityfrom the lamp. The phototransducer interprets this relatively low levelof incident light during lamp warm-up following turn-on in the samemanner as it does when the normal, relatively high intensity level lightbeam is interrupted by a moving article on the conveyor, and as aconsequence, falsely activates the material dispenser to dispensematerial when in fact no article is on the conveyor. Dispensing ofmaterial when an article is not on 5 the conveyor causes the dispensedmaterial to be deposited on the conveyor itself which, for obviousreasons, is undesirable.

In accordance with certain principles of this invention the foregoingproblem involving false triggering of the photosensing dispenser controlcircuit following initial turn-on is obviated by altering, for a briefperiod following turn-on and while the incandescent lamp filament heatsup, a reference voltage against which the phototransducer output iscompared to determine whether or not the light beam has beeninterrupted, whereby the normal relationship of phototransducer outputand reference voltage associated with a noninterrupted beam ofrelatively high intensity from a fully heated filament is maintainedeven though the beam has in fact not yet reached its normal, relativelyhigh intensity level. For example, in a preferred form of the inventionthe reference voltage is temporaily increased to avoid false triggeringsince the phototransducer output is such that it would normally increasewhen incident with less light, as occurs when a normal intensity lightbeam is interrupted by an article. In this way the increased output ofthe phototransducer temporarily occurring after turn-on does not exceedthe reference voltage which has been temporaily increased during turn-onin accordance with this invention.

In a preferred form of the invention, temporary alteration of thereference voltage against which the phototransducer output is comparedto avoid false triggering during turn-on is achieved by interconnectinga capacitor between the reference voltage terminal and the circuit powersupply. Immediately following turn-on and prior to the time thecapacitor has an opportunity to fully charge, there is a negligiblevoltage drop across the capacitor with the result that the referenceterminal is at the same voltage as the power supply, namely, at anartificially high voltage, which voltage exceeds the temporarily highvoltage output from the phototransducer immediately following lampenergization. As the capacitor charges following turn-on, the voltage ofthe reference terminal decreases. However, the rate of the decrease isselected such that during the transition period when the lamp intensityis building up the phototransducer output at all times will be less thanthe reference voltage, thereby avoiding false triggering. Thus, byutilization of a capacitor connected to the reference terminal theproblem of false triggering upon turn-on has been eliminated. Further,since the capacitor is not in the phototransducer circuit itself, butrather in the reference voltage circuit, the response of thephototransducer is not slowed down by capacitive delay effects.

False triggering, resulting in the undesired discharge of material inthe absence of an article on the conveyor, is also a problem duringturn-off of the photosensing control circuitry.

Specifically, as a consequence of turn-off, the incandescent lamp isde-energized causing the intensity of light incident on aphototransducer to drop. This decrease in light intensity on thephototransducer, insofar as the phototransducer is concerned, isinterpreted as an interruption of the light beam by an article moving onthe conveyor, with the result that the control circuit is cycled.

Under normal conditions, that is, when the light beam is interrupted byan article moving on the conveyor and the control circuit cycled, anelectronic switch, such as a transistor in series with the valveactuator, for example, a solenoid, is placed in a conductive condition,allowing current to flow from the power supply to the solenoid,energizing the solenoid, in turn actuating the material dispenser. Sincethe power supply for the solenoid includes a smoothing capacitor toremove the ripple from the full-wave rectified output of the typicalbridge rectifier circuit fed with conventional 60Hz a.c. power, thepower supply is capable of storing sufficient energy in capacitive formto energize the solenoid when the circuit is falsely cycled due to thedecreased light intensity on the phototransducer present when thecircuit is de-energized. Thus, the combination of capacitively storedenergy and the decreasing light intensity incident on thephototransducer when the circuit is turned off, causes the solenoid tobecome energized, dispensing material when in fact an article is notpresent on the conveyor.

Accordingly, it has been a further objective of this invention toobviate the false triggering and consequence undesired dispensing ofmaterial occasioned by turning off a photosensing control circuit. Inaccordance with certain additional principles of this invention, thisobjective has been accomplished by connecting an auxiliary switch in theenergization path of the solenoid, which switch is operated jointly withthe ON/- OFF switch of the control circuit. When the ON/OFF switch forthe control circuit is placed in an open circuit to de-energize thecontrol circuit, the auxiliary switch in the energization path of thesolenoid is placed in open-circuit condition, preventing energization ofthe solenoid with capacitively stored energy, which would otherwise tendto occur when the control circuit is cycled by the decreased lightincident on the phototransducer occasioned by de-energization of theincandescent lamp upon turn-off. In an alternative form of the inventionthe auxiliary switch, instead of being connected in the energizationpath of the solenoid, is connected across the smoothing capacitor andplaced in a closed-circuit condition simultaneously with theopencircuiting of the main ON/OFF switch. When so placed and operated,the auxiliary switch discharges the capacitor through a path other thanthe solenoid when the control circuit is turned off and cycled by thereduced light incident on the phototransducer caused by de-energizationof the incandescent lamp. Thus, the mere addition of an auxiliaryswitch, in either the energization path of the solenoid or to dischargethe smoothing capacitor, eliminates energization of the solenoid bycapacitively stored energy which would otherwise tend to result when thecontrol circuit is cycled as a consequence of the reduced light incidenton a phototransducer, when the incandescent lamp is deenergized byopen-circuiting of the main ON/OFF switch.

These and other advantages, features and objectives of the inventionwill become more readily apparent from a detailed description of theinvention in which the single figure is a diagrammatic view, partiallyin perspective, of a material dispensing system incorporating thecontrol circuit of this invention.

General Description The control circuit of this invention can be used ina variety of applications wherein it is desired to control a device inresponse to interruption of a light beam. However, for the purposes ofclarity and ease of understanding, the control circuit of this inventionis described in connection with a preferred environment in which it isutilized to control the application of glue to cartons moving on anendless belt conveyor, which cartons interrupt a light beam to effectdispensing as they move beneath a glue dispensing valve.

With reference to the FIGURE depicting the preferred embodiment, anendless conveying belt 10 is included, the upper section of which isdriven in the direction of arrow 11 by suitable motor means (not shown)which are drivingly connected to one or both of the rolls [2, 12 overwhich the belt trains. Disposed above the belt 10 at a suitable pointalong its length is a material dispensing valve 13 connected via conduit14 to a source of material (e.g., glue) to be dispensed 15. The sourceof material 15 is preferably pressurized to facilitate flow through theconduit 14 and dispensing valve 13 when the valve is switched from aclosed condition to an open condition. The valve 13 is provided with amovable flow control member (not shown) positionable between a closedposition in which material is not dispensed and an open position inwhich material is dispensed. Movement of the valve flow control memberbetween its open and closed positions is accomplished by anelectromechanical actuator 16, the mechanical output of which isconnected via suitable means shown schematically by dotted line 17. Tocontrol the electromechanical actuator 16, and hence the dispensing ofglue from valve 13, a control circuit 22, to be described in detailhereafter, is provided. Control circuit 22 includes, among other things,a source of light 24 and a phototransducer 25 located on opposite sidesof the conveyor belt 10 such that a beam of light 26 emanating from thelamp 24, which is incident on the phototransducer 25, is interrupted bya moving article 20, such as a box having a flap to which glue is to beapplied, when it arrives beneath valve 13.

In operation, when the leading edge of the box 20 moving on the conveyorbelt 10 in the direction of arrow 1] interrupts the light beam 26, thephototransducer 25, which is normally incident with light from the lamp24 at a relatively high intensity, is incident with ambient light onlywhich is at a much lower intensity level than existed prior tointerruption of the beam. The change in level of intensity of lightincident on the phototransducer 25 causes the control circuit 22 toenergize the electromechanical actuator 16, preferably for apredetermined interval, such as one second. Energization of theelectromechanical actuator 16 causes movement of its mechanical output17, in turn switching the flow control member of the dispensing valve 13from a closed condition to an open condition which, for the duration ofthe predetermined energization interval of the electromechanicalactuator 16, causes adhesive to be dispensed from the valve forapplication to the flap of the box 20.

Detailed Description The lamp 24, which directs a beam of light 26across reasonably intense source of light to overcome ambient lightingeffects, a lamp of the incandescent type. A 6.3- volt, No. 12incandescent lamp marketed by General Electric Company has been foundsatisfactory in applications wherethe distance between lamp andphototransducer, which is dictated by the width of the belt measured ina direction transverse to its length, is approximately 15 inches, andthe ambient lighting conditions are equivalent to those generally foundin manufacturing plants. The phototransducer 25 is preferably of thetype having a resistance which varies as a function of incident light.In practice, it has been found that a phototransducer is satisfactoryhaving a resistance in the meg-ohm range when in a dark" condition,i.e., at low incident light intensity when the beam 26 is interrupted,and a resistance in the range of 2k-5k ohms when in a light condition,i.e., when incident with an uninterrupted beam of light of relativelyhigh intensity from the lamp 24. A suitable phototransducer is marketedby Clairex Electronics, Inc., designated Model No. CL603A.

The lamp 24 is energized from a step-down transformer 28 which has itsprimary winding 28A connected to a conventional l-volt 60Hz. a.c. powersupply 30 via lines 31 and 32. An ON/OFF switch 33 is connected in line32 between the a.c. power supply 30 and the secondary winding 28A oftransformer 28. Transformer 28 has a secondary winding 288 which isconnected to the lamp 24 via lines 35 and 36. The transformer 28 stepsdown the l20-volt a.c. power from supply 30 to 6.3-volt a.c. forenergization of the lamp 24.

The remaining components of the control circuit 22, including thephototransducer 25, a threshold detector 37 incorporating a photocelltrigger amplifier 38 and a single-shot 40, and an electronic switch forcontrolling current flow through the electromechanical actuator 16, arepowered by a transformer 42, full-wave rectifier 44, smoothing capacitor46 and voltage regulator 49. Transformer 42 includes a primary winding42A which is connected across the conventional a.c. power supply 30through the ON/OFF switch 33 via lines 31 and 32. The secondary winding42B of the transformer 42 is connected to the input of the full-waverectifier 44. The transformer 42 steps/down the l20-volt a.c. power fromthe supply 30 to 28 volts a.c. for input to the fullwave rectifier 44.The full-wave rectifier 44 is a conventional bridge-type rectifier whichprovides full-wave rectification for the a.c. power input from thestepdown transformer 42. To remove the ripple in the fullwave rectifiedpower output from the rectifying bridge 44, the smoothing capacitor 46is connected to the rectifier output, providing across line 48 andgrounded line 47 substantially ripple-free unidirectional, or d.c.,power.

The voltage regulator 49 is of the conventional series regulating typefor providing 26-volt d.c. regulated power on regulator output line 50,and l5-volt d.c. regulated power on regulator output line 52. As thoseskilled in the art understand, a voltage regulator of the series-typeincludes a variable impedance 49A, which in this case is a Darlingtontransistor circuit, in series between regulator input line 48 andregulator output line 50. A voltage comparator in the form of atransistor 49B alters the impedance of series transistor circuit 49A asthe result of a comparison between a reference voltage established by aZener diode 49C and the regulated output voltage on line 50 as reflectedby the output 49D of a voltage divider 49E responsive to the volt age onregulator output line 50. The regulated output voltage on line 52, whichis approximately 11 volts below that on regulated output line 50, isprovided by a voltage dropping transistor 49F connected between lines 50and 52. Resistor 49G combines to provide bias for transistor 49F and toprovide current limiting for Zener diode 49C. A capacitor 49H connectedbetween regulated voltage line 50 and ground line 47 provides additionalsmoothing of the regulated output from the regulator 49.

The electromechanical actuator 16, which preferably takes the form of asolenoid valve having a movable armature shown schematically by dottedline 17, is connected between a grounded line 54 and the regulatedvoltage line 50 via a switch 55, a resistor 56, and an electronic switch53. Resistor 56 provides a current limiting function should the solenoidl6 become shortcircuited. The electronic switch 53, which preferablytakes the form of a transistor, facilitates energization of the solenoid16 when the threshold detector 37 provides an output thereto on line 57in response to interruption of the light beam 26 in the manner to bedescribed. A diode 58 is connected in series with a Zener diode 59, bothof which are connected across the solenoid 16 to protect the transistorswitch 53. Zener diode 59 performs the additional function of notslowing down the response of the solenoid to controlled current flowthrough the transistor switch 53, which would otherwise tend to occur byreason of utilization of diode 58.

The switch 55, which is also in series with the energization path ofsolenoid l6 and the electronic switch 53, is operated jointly with theON/OFF switch 33. Switch 55, when the ON/OFF switch 33 is transferredfrom a closed-circuit to an open-circuit condition, prevents energycapacitively stored in smoothing capacitors 46 and 49H from beingdischarged through the solenoid 16 when the electronic switch 53 isplaced in a conductive state by the detector 37 which occurs, in amanner to be described, as a consequence of de-energization of the lamp24 when ON/OFF switch 33 is opened, causing the phototransducer 26 to godark. Were switch 55 omitted, when the control circuit 22 isde-energized by opening switch 33, the solenoid 16 would be momentarilyenergized, resulting in unwanted dispensing of adhesive from valve 13.

Specifically, when the ON/OFF switch 33 is switched to an open-circuitcondition, power is removed from the lamp 24, which lamp then ceases toirradiate the phototransducer 25. Since the detector 37 operates toactivate the electronic switch 53 for energizing the solenoid 16 whenthe phototransducer 25 goes dark," which normally occurs when the beam26 is interrupted by an article 20 on the conveyor 10, de-energizationof the lamp 24 as a consequence of removing power from the controlcircuit via switch 33 is interpreted by the detector 37 as aninterruption of the light beam, which detector then responds to providean output on line 57 to render electronic switch 53 conductive. Eventhough ON/OFF switch 33 is open, since energy is capacitively stored insmoothing capacitors 46 and 49H, sufficient energy is available forcycling the detector 37 and solenoid 16 when the lamp 24 ceases to beilluminated upon opening of ON/OFF switch 33.

Inclusion of the switch 55, which is actuated jointly with switch 33,eliminates energization of the solenoid 16 when the ON/OFF switch 33 isopened and the lamp 24 darkened, simulating interruption of the beam 26by an article on the conveyor. Specifically, energy capacitively storedin the smoothing capacitors 46 and 49H is prevented from flowing to thesolenoid 16, when the electronic switch 53 is falsely cycled bydeenergization of the lamp 24 occasioned by opening ON/OFF switch 33,which deenergization of the lamp 24, as indicated, simulatesinterruption of the light beam 26 by an article 20 on the conveyor 10.

While the switch 55 has been shown connected in series between line 50and current limiting resistor 56, those skilled in the art willunderstand that switch 55 could be connected anywhere in theenergization path of the solenoid 16 between line 50 and grounded line54. Alternatively, instead of placing switch 55 in the energization pathof the solenoid 16 between lines 50 and 54, the energy capacitivelystored in smoothing capacitor 46 could be by-passed with respect to thesolenoid 16 when the detector is falsely cycled by deenergization of thelamp 24 when the switch 33 is opencircuited. Specifically, the switch 55could be replaced by two switches 55 and 55" placed in series withresistors R and R, respectively, across the smoothing capacitors 46 and49H, respectively, as shown in dotted lines. With switches 55 and 55"placed across smoothing capacitors 46 and 49H, rather than a switch 55in series with the solenoid 16, when the ON/OFF switch 33 is placed inan open-circuit condition the switches 55 and 55" would be placed in aclosed-circuit condition to discharge the capacitors 46 and 49H toground via resistors R and R". Thus, when the detector 37 is falselycycled to actuate the electronic switch 53 and place it in a conductivecondition as a consequence of lamp 24 being de-energized by opening ofON/OFF switch 33, energy capacitively stored in capacitors 46 and 491-1will not be discharged through the solenoid 16 to operate valve 14, butrather will be discharged to ground 47 via resistors R and R.

The phototransducer trigger amplifier 38, which forms the first stage ofthe threshold detector 37, principally includes an operational amplifier60 having a reference voltage input terminal 60A, a sampling votageinput terminal 608, and an output terminal 60C. So long as the referencevoltage input to terminal 60A exceeds the signal input to sampleterminal 608, the output at terminal 60C is at a relatively high level.However, should the sample voltage input to terminal 60B become morepositive than the reference voltage input to terminal 60A, the output atterminal 60C is reduced to a relatively low level. An operationalamplifier found to operate satisfactorily is marketed by FairchildSemiconductor Company, designated Model UA741 described at pages 107-113 of Fairchild Linear Integrated Circuits Data Catalog, November 1971edition.

The reference terminal 60A of the amplifier 60 is connected to themidpoint of a voltage divider consisting of resistors 62 and 63connected between ground line 54 and the regulated -volt d.c. line 52,providing a 7% volt d.c. reference level. The sampling terminal 608 ofthe operational amplifier 60 is connected to a voltage divider whichincludes a resistor 68 constituting one section of the voltage divider,and a resistor 69 connected in parallel with the phototransducer 26which collectively constitute the other portion of the voltage divider.

Under normal conditions, that is, when the lamp 24 is energized and thebeam 24 incident on phototransducer 25, providing the phototransducerwith a resistance of 2k-5k ohms, the line 70 input to sampling terminal60B is at approximately 2 volts. Under such conditions of lampenergization and beam continuity, the 7 /2 volt reference signal inputto operational amplifier terminal 60A is more positive than the normal2-volt phototransducer signal level input to operational amplifierterminal 608, with the result that the output from the operationalamplifier on line 60C is at a relatively high value. However, should thelight beam 26 from source 24 incident on phototransducer 25 beinterrupted by, for example, passage of an article on the conveyor 10between the lamp and phototransducer, or light beam interruptionsimulated by de-energization of the lamp, the resistance of thephototransducer 25 shifts to a value exceeding 1 meg-ohm, providing online 70 to the operational amplifier sampling terminal 60B a voltage ofapproximately 14 volts. Under these input conditions wherein the voltageof sampling terminal 60B exceeds the voltage of reference terminal 60A,the output on line 60C shifts from a relatively high level to arelatively low level.

A diode and resistor 76 series-connected between ground line 54 and theregulated 15-volt d.c. line 52, in combination with a capacitor 77connected between operational amplifier line 60C and the junction ofdiode 75 and resistor 76, function to differentiate the downshift insignal level at terminal 60C which accompanies interruption of the lightbeam 26, providing on line 78 a negative-going voltage spike each timethe light beam is interrupted by passage of an article between the lampand phototransducer, or each time light beam interruption is simulatedas when, for example, the lamp 24 is de-energized by open-circuiting theswitch 33.

The single-shot circuit 40, preferably is a linear integrated circuitconnected in a monostable mode of operation, having an input terminal40A, is responsive to the differentiated output from the operationalamplifier 60 present on line 78. Each time a negative-going spike isinput to the single-shot 40 on line 78, a positive pulse of selectivelyvariable duration is output from the single-shot on line 79. Theduration of the positive pulse output from the single-shot on line 79 asa consequence of each negative-going spike input thereto on line 78 canbe varied by varying the magnitude of a control signal level input tothe single-shot via a potentiometer 80 connected between a controlterminal 40B of the single-shot and a source of positive potential.Preferably the adjustment is such that the duration of the output pulseon line 79 is approximately in the range of 0.01 to 1.0 seconds.

The positive pulse output on line 79 from the singleshot 40 each time anegative-going spike is input to the single-shot on line 40A from theoperational amplifier 60 which, as noted, occurs each time the lightincident on the phototransducer 25 decreases, as occurs, for example,when the light beam 26 is interrupted by an article moving on a conveyoror the lamp 24 is deenergized by opening switch 33, is input to the baseof transistor switch 53 by a coupling resistor 82. The transistor switch53 which is normally non-conducting, that is, is not conducting absent apositive pulse input thereto from the single-shot 40, is renderedconductive by the positive pulse output from the single-shot. Conductionof transistor switch 53 completes a portion of the energization pathbetween ground line 54 and the regulated voltage line 50 for thesolenoid 16, the other portion of the path being completed by switch 55which is closed when the control circuit is energized by placement ofswitch 33 in the closed condition. Conduction of transistor switch 53 inresponse to a positive pulse input from the single shot 40, assumingswitch 55 is also closed, causes the solenoid 16 to be energized for theduration of the single-shot output pulse. Energization of the solenoid16, in a manner heretofore described, actuates valve 13 to dispenseadhesive from the source 15 to the article positioned therebeneath.

When ON/OFF switch 33 is switched to an open circuit condition, lamp 24is de-energized causing the level of light incident on phototransducer25 to decrease. As a consequence, the voltage input to terminal 608 ofthe operational amplifier on line 70 shifts from its normal level ofapproximately 2 volts to approximately 14 volts, in turn producing anegative-going spike input at terminal A of the single-shot 40 which inturn provides a positive pulse on line 57 to the electronic switch 53.Thus, the operational amplifier 60 and the single-shot 40 are falselycycled when the lamp 24 is de-energized by opening switch 33, producingan output from detector 37 to switch 53 similar to that which occurswhen the enregized lamp 24 has its beam 26 interrupted by an article inthe conveyor.

The switching of transistor switch 53 to a conductive state in responseto the false cycling of the operational amplifier 60 and single-shot 40when the lamp 24 is deenergized would, were it not for the opening ofswitch 55 concurrently with the opening of ON/OFF switch 33, cause theenergization of solenoid 16, since energy capacitively stored insmoothing capacitors 46 and 49H would, even though the switch 33 hasbeen opened, discharge through the solenoid 16 causing it to beenergized and actuate the valve 13. Actuation of the solenoid l6, andhence the valve 13, in response to deenergizing the lamp 24 when theswitch 33 is opened is avoided in accordance with principles of thisinvention by utilization of switch 55 in series in the energization pathof solenoid 16, which switch 55 is open simultaneously with opening ofswitch 33, thereby preventing discharge of capacitively stored energythrough the solenoid 16.

In accordance with an alternative form of this invention, energizationof the solenoid 16 in response to false triggering of the operationalamplifier 60 and singleshot 40 when the switch 33 is opened and the lamp24 de-energized, is avoided by location of the switches 55 and 55"across the capacitors 46 and 49H rather than placing a switch in serieswith the energization path of the solenoid 16. With the switches 55' and55" such that they are normally open, but are closed when the mainswitch 33 is opened, energy capacitively stored in the capacitors 46 and491-! will discharge through resistors R and R" to ground when the mainswitch 33 is opened.

Another potential source of false cycling of the solenoid 16 occurs whenthe control circuit 22 is initially energized by closure of the switch33. Specifically, when the switch 33 is closed, energizing the voltageregulator 49 and the lamp 24, power is available on lines 50 and 52 on avirtually instantaneous basis energizing the operational amplifier 60and single-shot 40 and the circuitry associated therewith. Likewise,power is instantaneously available for energizing the solenoid 16 shouldthe transistor switch 53 be rendered conduc- 5 tive since switch 55 isclosed simultaneously with the closure of switch 33. However, the lamp24 at the moment of closure of the switch 33 is not instantaneouslyrendered operative to produce light at full light intensity, but ratherthe intensity of the lamp 24 increases gradually from zero intensity toits operating level over an interval of approximately 100 milliseconds.While the intensity of the lamp 24 is increasing following closure ofswitch 33, but prior to its reaching full intensity, the phototransducer25 is incident with a level of light below normal, that is, with a levelof light associated with interruption of the beam 26 by an article onthe conveyor. Under such conditions, the resistance of thephototransducer 25 is in the meg-ohm region placing a signal on line 70of a relatively high level which, initially following closure of theswitch 33, is more positive than the 7% volt level which is normallypresent on line 64. Were the level of the signal on line 70 immediatelyfollowing closure of switch 33 permitted to exceed the level of thereference signal normally present on line 64, the operational amplifierwould be falsely triggered to provide at its terminal 60C a relativelylow level signal associated with interruption of the full intensitylight beam 26, which in turn would falsely trigger the single-shot 40,energize the electronic transistor switch 53, and complete theenergization path for the solenoid 16 to cycle the solenoid and thevalve 13.

However, and to avoid false triggering of the operational amplifier andsingle-shot immediately following energization of the lamp 24 by closureof the switch 33 when, at least initially, the lamp 24 has a relativelylow intensity, a capacitor 66 is connected between the 15- volt d.c.regulator line 52 and the sample terminal 60A of the operationalamplifier 60. When switch 33 is initially closed and capacitor 66uncharged, the voltage of line 64 is very close to the l5-volt potentialof line 52. Since the potential of line 64 under these circum stancesexceeds that of line existing when the intensity of the lamp 24 isrelatively low, the output of the operational amplifier at terminal 60Cis at a relatively high level characteristic of that present when thefull intensity lamp beam is not interrupted by an article on theconveyor. Following closure of the switch 33 and as the capacitor 66begins to charge, the signal level on line 64 drops from theapproximately 15-volt level'on line 52 to 7% volt reference levelestablished by the voltage divider 62, 63 when the capacitor 66 is fullycharged. The size of the capacitor 66 and resistors 62 and 63 should beselected such that the decreasing signal level on line 64 associatedwith the gradual charging of capacitor 66 following closure of switch 33remains above the level of the phototransducer signal on line 70following closure of switch 33 associated with the gradual decrease inresistance of the phototransducer 25 as the intensity of the lamp 24gradually increases to its steady state level. Thus, the capacitor 66avoids false triggering of the operational amplifier 60 and single-shot40 which, via transistor switch 53, would cycle the solenoid l6 and thevalve 13 when the switch 33 is closed and the incandescent lamp 24 hasnot reached its full intensity.

False triggering of the operational amplifier 60 and single-shot 40 uponclosure of the switch 33 due to the fact that the lamp 24 does not reachits full intensity until lapse of a specified warm up time could havebeen avoided by connecting the capacitor 66 between the phototransducerinput terminal 608 and ground line 54, rather than between the referenceterminal 60A and positive line 52. By so doing, line 70 would be kept atan artificially low potential immediately following closure of switch 33while the lamp intensity 24 is building up, with the result thatreference line 64, which by virtue of voltage divider 63, 63 is at 7 /2volts, exceeds the signal level on line 70, preventing false triggeringof the operational amplifier 60. However, had the capacitor 66 beenconnected between ground line 54 and terminal 608 of the operationalamlifier 60, rather than as in the preferred embodiment wherein it isconnected between the reference terminal 60A of the operationalamplifier and the positive line 52, the response time of thephototransducer 25 to changes in incident light when the beam is brokenby an article on the conveyor would have been deleteriously affected,which is not the case when the capacitor 66 is connected between thereference line 64 and the positive bus 52 as in the preferred embodimentof this invention.

Having described the invention, what is claimed is:

l. A control circuit for energizing an electromechanical actuator tooperate a valve in a material dispensing mode in response tointerruption of a light beam occur ring in timed relation to movement ofan article past a dispenser associated with said valve, said controlcircuit comprising:

a rectifier circuit connectable to an ac. source for providing rectifiedcurrent,

a capacitor connected to said rectifier for smoothing said rectifiedcurrent,

an electronic switch connected between said capacitor and saidelectromechanical actuator, said switch operable in response to acontrol signal to switch to a conductive condition to facilitiateenergizing said electromechanical actuator for operat ing said valve todispense material to said article,

a phototransducer,

a lamp energizable to direct a light beam to said phototransducer,

first switch means connecting said lamp and said rectifier to said a.c.source for selectively energizing said lamp and rectifier when actuated,

a detector circuit connected between said phototransducer and saidelectronic switch for providing, in response to a decrease in lightincident on said phototransducer, a control signal to said electronicswitch for switching it to said conductive condition to facilitateenergizing said electromechanical actuator for operating said valve todispense material to said article, and

second switch means connected in series with said electromechanicalactuator and said electronic switch, said second switch means beingjointly actuable with said first switch means to prevent energization ofsaid electromechanical actuator by energy stored in said capacitor whensaid electronic switch is rendered conductive by a control signalproduced by said detector when said first switch is dc-actuated and saidlamp deenergized, reducing the light incident on said phototransducer,

2. A control circuit for energizing an electromechanical actuator tooperate a valve in a material dispensing mode in response tointerruption ofa light beam occurring in timed relation to movement ofan article past a dispenser associated with said valve, said controlcircuit comprising:

a phototransducer,

an incandescent lamp energizable to direct a light beam to saidphototransducer, the intensity of said lamp increasing gradually from alevel less than normal when initially energized and reaching normalintensity after a predetermined interval,

said phototransducer providing a normal output sig' nal of a first levelwhen incident with light of normal intensity from said lamp andproviding an output signal of second level when incident with light fromsaid lamp of intensity less than normal,

first switch means connecting said lamp and said power supply forselectively energizing said lamp when actuated,

a reference voltage source providing a reference voltage,

an operational amplifier having an input terminal connected to saidreference voltage source, said operational amplifier providing a controlsignal to said electronic switch to render it conductive to actuate saidelectromechanical actuator for operating said valve in a materialdispensing mode in response to a predetermined voltage relationshipexisting across said input and reference terminals, which predeterminedrelationship exists when said phototransducer is at said second leveland said reference terminal is at said reference level, and meansconnected to said reference terminal for altering, during saidpredetermined interval, the voltage level at said reference terminal toprevent, while the intensity of said lamp is gradually increasing tonormal, said predetermined voltage relationship from existing acrosssaid input and reference terminals, which would otherwise result byreason of said phototransducer output being at said level due to saidlamp not yet having reached normal intensity, whereby production offalse control signals are avoided as an incident to energizing saidlamp.

3. A control circuit for energizing an electromechanical actuator tooperate a valve in a material dispensing mode in response tointerruption of a light beam occurring in timed relation to movement ofan article past a dispenser associated with said valve, said controlcircuit comprising:

a rectifier circuit connectable to an ac. source for providing rectifiedcurrent,

a capacitor connected to said rectifier for smoothing said rectifiedcurrent,

an electronic switch connected between said capacitor and saidelectromechanical actuator, said switch operable in response to acontrol signal to switch to a conductive condition to facilitateenergizing said electromechanical actuator for operating said valve todispense material to said article,

a phototransducer,

an incandescent lamp energizable to .direct a light beam to saidphototransducer, the intensity of said lamp increasing gradually from alevel less than normal when initially energized and reaching normalintensity after a predetermined interval,

said phototransducer providing a normal output signal of a first levelwhen incident with light of normal intensity from said lamp andproviding an output signal of second level when incident with light fromsaid lamp of intensity less than normal,

first switch means connecting said lamp and said rectifier to said a.c.source for selectively energizing said lamp and rectifier when actuated,

a reference voltage source providing a reference voltage,

an operational amplifier having an input terminal connected to saidreference voltage source, said operational amplifier providing a controlsignal to said electronic switch to render it conductive to actuate saidelectromechanical actuator for operating said valve in a materialdispensing mode in response to a predetermined voltage relationshipexisting across said input and reference terminals, which predeterminedrelationship exists when said phototransducer is at said second leveland said reference terminal is at said reference level,

a capacitor connected to said rectifier for smoothing said rectifiedcurrent, and

second switch means connected in series with said electromechanicalactuator and said electronic switch, said second switch means beingjointly actuable with said first switch means to prevent energization ofsaid electromechanical actuator by energy stored in said capacitor whensaid electronic switch is rendered conductive by a control signalproduced by said detector when said first switch is de-actuated and saidlamp is de-energized, reducing the light incident on saidphototransducer.

4. The circuit of claim 2 wherein said reference terminal voltage levelaltering means includes a capacitor connected between said power supplyand said reference terminal for effectively short-circuiting saidreference terminal to said power supply to vary said reference terminalinput voltage in a manner compensating for transient effects on thephototransducer output signal when said lamp intensity is increasing tonormal following lamp energization.

5. A control circuit for energizing an electromechanical actuator tooperate a valve in a material dispensing mode in response tointerruption of a light beam occurring in timed relation to movement ofan article past a dispenser associated with said valve, said controlcircuit comprising:

a phototransducer having a resistance which varies inversely with theintensity of light incident thereon,

an incandescent lamp energizable to direct a light beam to saidphototransducer, the intensity of said lamp increasing gradually from alevel less than normal when initially energized and reaching normalintensity after a predetermined interval,

said phototransducer providing a relatively low output signal whenincident with light of normal intensity from said lamp and providing anoutput signal of relatively high potential when incident with light fromsaid lamp of intensity less than normal,

a reference voltage source providing a reference voltage intermediatesaid relatively low and high potentials associated with normal and lessthan normal incident intensities on said phototransducer, respectively,

an operational amplifier having an input terminal connected to saidreference voltage source, said operational amplifier providing a controlsignal to said electronic switch to render it conductive to actuate saidelectromechanical actuator for operating said valve in a materialdispensing mode only when said voltage at said input terminal exceedsthe voltage at said reference terminal,

a capacitor connected between said reference terminal and said powersupply for increasing, during said predetermined interval, the voltagelevelat said reference terminal to prevent, while the intensity of saidlamp is gradually increasing to normal, the phototransducer output atsaid input terminal from exceeding the voltage at said referenceterminal, which would otherwise result by reason of said phototransduceroutput being at said relatively high potential in excess of saidreference potential due to said lamp not yet having reached normalintensity, whereby production of false control signals are avoided as anincident to energizing said lamp.

6. A control circuit for energizing an electromechanical actuator tooperate a valve in a material dispensing mode in response tointerruption of a light beam occurring in timed relation to movement ofan article past a dispenser associated with said valve, said controlcircuit comprising:

a rectifier circuit connectable to an ac. source for providing arectified current,

a capacitor connected to said rectifier for smoothing said rectifiedcurrent,

an electronic switch connected between said capacitor and saidelectromechanical actuator, said switch operable in response to acontrol signal to switch to a conductive condition to facilitateenergizing said electromechanical actuator for operating said valve todispense material to said article,

a phototransducer,

a lamp energizable to direct a light beam to said phototransducer,

first switch means connecting said lamp and said rectifier to said a.c.source for selectively energizing said lamp and rectifier when actuated,

a detector circuit connected between said phototransducer and saidelectronic switch for providing, in response to a decrease in lightincident on said phototransducer, a control signal to said electronicswitch for switching it to said conductive condition to facilitateenergizing said electromechanical actuator for operating said valve todispense material to said article, and

means connected to said capacitor and jointly actuable with said firstswitch means to prevent energization of said electromechanical actuatorby energy stored in said capacitor when said electronic switch isrendered conductive by a control signal produced by said detector whensaid first switch is deactuated and said lamp de-energized, reducing thelight incident on said phototransducer.

7. The control circuit of claim 6 wherein said energization preventionmeans includes a normally open second switch adapted to be closed whensaid first switch is de-actuated, said second switch being connected tosaid capacitor for discharging said capacitor through a path excludingsaid electromechanical actuator when said second switch is closedcoincident with deactuation of said first switch.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,52,414 DATED January 21, 1975 lNVENTOMS) Harvey R. Algeri It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

' In the Specification:

Col. 1', Line 56, change "atrributable" to --attributable-- In theClaims: I

Col. 12 Line 42, insert "second" between the words "said" and "level".

Signed and Scaled this D seventh Day of 0ct0rber1975 [SEAL] 1 Arrest: I

RUTH MQSON c. MARSHALL DANN Arleslmg Ojjicer Commissioner of Parents andTrademarks

1. A control circuit for energizing an electromechanical actuator tooperate a valve in a material dispensing mode in response tointerruption of a light beam occurring in timed relation to movement ofan article past a dispenser associated with said valve, said controlcircuit comprising: a rectifier circuit connectable to an a.c. sourcefor providing rectified current, a capacitor connected to said rectifierfor smoothing said rectified current, an electronic switch connectedbetween said capacitor and said electromechanical actuator, said switchoperable in response to a control signal to switch to a conductivecondition to facilitiate energizing said electromechanical actuator foroperating said valve to dispense material to said article, aphototransducer, a lamp energizable to direct a light beam to saidphototransducer, first switch means connecting said lamp and saidrectifier to said a.c. source for selectively energizing said lamp andrectifier when actuated, a detector circuit connected between saidphototranSducer and said electronic switch for providing, in response toa decrease in light incident on said phototransducer, a control signalto said electronic switch for switching it to said conductive conditionto facilitate energizing said electromechanical actuator for operatingsaid valve to dispense material to said article, and second switch meansconnected in series with said electromechanical actuator and saidelectronic switch, said second switch means being jointly actuable withsaid first switch means to prevent energization of saidelectromechanical actuator by energy stored in said capacitor when saidelectronic switch is rendered conductive by a control signal produced bysaid detector when said first switch is de-actuated and said lampdeenergized, reducing the light incident on said phototransducer.
 2. Acontrol circuit for energizing an electromechanical actuator to operatea valve in a material dispensing mode in response to interruption of alight beam occurring in timed relation to movement of an article past adispenser associated with said valve, said control circuit comprising: aphototransducer, an incandescent lamp energizable to direct a light beamto said phototransducer, the intensity of said lamp increasing graduallyfrom a level less than normal when initially energized and reachingnormal intensity after a predetermined interval, said phototransducerproviding a normal output signal of a first level when incident withlight of normal intensity from said lamp and providing an output signalof second level when incident with light from said lamp of intensityless than normal, first switch means connecting said lamp and said powersupply for selectively energizing said lamp when actuated, a referencevoltage source providing a reference voltage, an operational amplifierhaving an input terminal connected to said reference voltage source,said operational amplifier providing a control signal to said electronicswitch to render it conductive to actuate said electromechanicalactuator for operating said valve in a material dispensing mode inresponse to a predetermined voltage relationship existing across saidinput and reference terminals, which predetermined relationship existswhen said phototransducer is at said second level and said referenceterminal is at said reference level, and means connected to saidreference terminal for altering, during said predetermined interval, thevoltage level at said reference terminal to prevent, while the intensityof said lamp is gradually increasing to normal, said predeterminedvoltage relationship from existing across said input and referenceterminals, which would otherwise result by reason of saidphototransducer output being at said level due to said lamp not yethaving reached normal intensity, whereby production of false controlsignals are avoided as an incident to energizing said lamp.
 3. A controlcircuit for energizing an electromechanical actuator to operate a valvein a material dispensing mode in response to interruption of a lightbeam occurring in timed relation to movement of an article past adispenser associated with said valve, said control circuit comprising: arectifier circuit connectable to an a.c. source for providing rectifiedcurrent, a capacitor connected to said rectifier for smoothing saidrectified current, an electronic switch connected between said capacitorand said electromechanical actuator, said switch operable in response toa control signal to switch to a conductive condition to facilitateenergizing said electromechanical actuator for operating said valve todispense material to said article, a phototransducer, an incandescentlamp energizable to direct a light beam to said phototransducer, theintensity of said lamp increasing gradually from a level less thannormal when initially energized and reaching normal intensity after apredetermined interval, said phototransducer providing a normal outputsignal of a first level when incident with light of normal intensityfrom said lamp and providing an output signal of second level whenincident with light from said lamp of intensity less than normal, firstswitch means connecting said lamp and said rectifier to said a.c. sourcefor selectively energizing said lamp and rectifier when actuated, areference voltage source providing a reference voltage, an operationalamplifier having an input terminal connected to said reference voltagesource, said operational amplifier providing a control signal to saidelectronic switch to render it conductive to actuate saidelectromechanical actuator for operating said valve in a materialdispensing mode in response to a predetermined voltage relationshipexisting across said input and reference terminals, which predeterminedrelationship exists when said phototransducer is at said second leveland said reference terminal is at said reference level, a capacitorconnected to said rectifier for smoothing said rectified current, andsecond switch means connected in series with said electromechanicalactuator and said electronic switch, said second switch means beingjointly actuable with said first switch means to prevent energization ofsaid electromechanical actuator by energy stored in said capacitor whensaid electronic switch is rendered conductive by a control signalproduced by said detector when said first switch is de-actuated and saidlamp is de-energized, reducing the light incident on saidphototransducer.
 4. The circuit of claim 2 wherein said referenceterminal voltage level altering means includes a capacitor connectedbetween said power supply and said reference terminal for effectivelyshort-circuiting said reference terminal to said power supply to varysaid reference terminal input voltage in a manner compensating fortransient effects on the phototransducer output signal when said lampintensity is increasing to normal following lamp energization.
 5. Acontrol circuit for energizing an electromechanical actuator to operatea valve in a material dispensing mode in response to interruption of alight beam occurring in timed relation to movement of an article past adispenser associated with said valve, said control circuit comprising: aphototransducer having a resistance which varies inversely with theintensity of light incident thereon, an incandescent lamp energizable todirect a light beam to said phototransducer, the intensity of said lampincreasing gradually from a level less than normal when initiallyenergized and reaching normal intensity after a predetermined interval,said phototransducer providing a relatively low output signal whenincident with light of normal intensity from said lamp and providing anoutput signal of relatively high potential when incident with light fromsaid lamp of intensity less than normal, a reference voltage sourceproviding a reference voltage intermediate said relatively low and highpotentials associated with normal and less than normal incidentintensities on said phototransducer, respectively, an operationalamplifier having an input terminal connected to said reference voltagesource, said operational amplifier providing a control signal to saidelectronic switch to render it conductive to actuate saidelectromechanical actuator for operating said valve in a materialdispensing mode only when said voltage at said input terminal exceedsthe voltage at said reference terminal, a capacitor connected betweensaid reference terminal and said power supply for increasing, duringsaid predetermined interval, the voltage level at said referenceterminal to prevent, while the intensity of said lamp is graduallyincreasing to normal, the phototransducer output at said input terminalfrom exceeding the voltage at said reference terminal, which wouldotherwise result by reason of said phototransducer output being at saidrelatively high potential in excess of said referenCe potential due tosaid lamp not yet having reached normal intensity, whereby production offalse control signals are avoided as an incident to energizing saidlamp.
 6. A control circuit for energizing an electromechanical actuatorto operate a valve in a material dispensing mode in response tointerruption of a light beam occurring in timed relation to movement ofan article past a dispenser associated with said valve, said controlcircuit comprising: a rectifier circuit connectable to an a.c. sourcefor providing a rectified current, a capacitor connected to saidrectifier for smoothing said rectified current, an electronic switchconnected between said capacitor and said electromechanical actuator,said switch operable in response to a control signal to switch to aconductive condition to facilitate energizing said electromechanicalactuator for operating said valve to dispense material to said article,a phototransducer, a lamp energizable to direct a light beam to saidphototransducer, first switch means connecting said lamp and saidrectifier to said a.c. source for selectively energizing said lamp andrectifier when actuated, a detector circuit connected between saidphototransducer and said electronic switch for providing, in response toa decrease in light incident on said phototransducer, a control signalto said electronic switch for switching it to said conductive conditionto facilitate energizing said electromechanical actuator for operatingsaid valve to dispense material to said article, and means connected tosaid capacitor and jointly actuable with said first switch means toprevent energization of said electromechanical actuator by energy storedin said capacitor when said electronic switch is rendered conductive bya control signal produced by said detector when said first switch isdeactuated and said lamp de-energized, reducing the light incident onsaid phototransducer.
 7. The control circuit of claim 6 wherein saidenergization prevention means includes a normally open second switchadapted to be closed when said first switch is de-actuated, said secondswitch being connected to said capacitor for discharging said capacitorthrough a path excluding said electromechanical actuator when saidsecond switch is closed coincident with de-actuation of said firstswitch.